Aquatic structures, in particular immersed marine structures that come in contact with water, especially sea water, have a tendency to become fouled by marine organisms. Antifouling and fouling-release paint systems are abundantly used for such structures, e.g. ships, buoys, watercraft structures, etc. in order to suppress settlement of such marine organisms, or to encourage their release.
Fouling-release coating systems for steel structures typically include three principal layers, namely an epoxy-based anticorrosive layer applied to the steel substrate, a fouling-release layer, and an intermediate layer, often referred to as a “tie-coat”, for establishing strong bonding between the otherwise incompatible epoxy-based anticorrosive layer and the polysiloxane-based fouling-release layer.
WO2005/033219 discloses a coating composition comprising at least two types of functional polysiloxane compounds selected from epoxy-functional polysiloxanes, amino-functional polysiloxanes, and particular adhesion promoting agents of the polysiloxane type.
EP 1 013 727 A1, U.S. Pat. Nos. 6,391,464 and 6,110,536 (General Electric Co.) disclose an epoxy-silicone adhesive paint as a tie-coat for a fouling-release coating. The paint comprises 80-85% by weight of an epoxy resin paint, and 15-20% by weight of a silicon-based adhesion promoter. The silicon adhesive promoter comprises a volatile hydrocarbon solvent, a partially condensed organosilicate, a solubilized metallic catalyst, and an aminoalkyltrialkoxysilane.
EP1670866 discloses a fouling release tie-coat composition.
Typically, tie-coat compositions have proven difficult to provide good adhesion at low temperatures at the interface between the primer or anticorrosive composition (typically an epoxy, acrylic or polyurethane coating) to the mainly polysiloxane based composition (typically a silicone based tie-coat or a silicone based topcoat). Blistering is also a problem and is often the cause of adhesion loss.
In view of the above, there is a need for improved or at least alternative tie-coat compositions for fouling-release coating. In particular, there is a need for tie-coat systems which are able to provide strong bonding between a surface and a polysiloxane based layer even at low application temperatures of the compositions.